Method for making a film with improved wettability properties

BACKGROUND OF THE INVENTION

The present invention relates generally to a method for making a film with a higher surface energy having improved wettability properties.

Condensing heat exchangers are employed in condensing furnaces to increase efficiency. The condensing heat exchanger cools the heating fluid to a temperature below the dew point. As the temperature drops below the dew point, a liquid condensate, water vapor, condenses from the heating fluid. As the liquid condensate condenses, heat is transferred from the water vapor to the air to be heated. As more heat is produced, the efficiency of the system is increased.

Polypropylene films are used to make laminated heat exchanger material. Most films have surface energies (30-40 dynes) that are considerably lower than the surface energy of water (78 dynes). Because the films have a considerably lower surface energy, the liquid condensate forms as droplets on the surface of the film, rather than spreading out as a thin film. The droplets can leave the film and enter the atmosphere. As the liquid condensate is slightly acidic, the formation of droplets is environmentally undesirable.

Liquid condensate also forms as droplets on air conditioner evaporator heat exchanger fin stock. The film applied to the aluminum fin is also of low surface energy. As air flows, the liquid condensate droplets can leave the surface of the film and enter the area which is to be cooled. Additionally, the droplets can increase the likelihood of corrosion of the fins.

Hence, there is a need in the art for a method for making a film with a higher surface energy having improved wettability properties.

SUMMARY OF THE INVENTION

The present invention relates to a method for making a film with a higher surface energy having improved wettability properties.

By increasing the surface energy of the film, the wettability of the film can be increased, improving heat transfer. The film can be made of any thermoplastic film which bonds to metal, such as polyolefin, polyester, polyetherketone, polyetheretherketone, polysulfone, polyethersulfone, polytetrafluoroethlyne, or fluorinatedhydrocarbon.

While the film is soft and heated, polar particulates are mechanically adhered to and embedded in the upper surface of the film. The particulate may be any polar material that embeds in and adheres to the upper surface of the film. The particulate is partially exposed and creates a polar surface. The polar particulate may be alumina, silica, zirconia, wollastonite, talc, titanium dioxide, or any other polar material. At the molecular level, the polar particulate is charged and has a positive portion and a negative portion. The positive portion and the negative portion of the polar particulates attract the polar water molecules which are also charged at the molecular level.

The metal surface of the heat exchanger is then coated with either an adhesive substance or a mixture of reactants that polymerize in situ. The cooled film is then laminated to the metal surface of the heat exchanger.

In another embodiment, the particulate is surface treated to either enhance adhesion of the particulate to the polymer or to enhance wettability.

In another embodiment, the particulate is pressed into a film coated with either an adhesive substance or a mixture of reactants that polymerize in situ.

Accordingly, the present invention provides a method for making a film with a higher surface energy having improved wettability properties.

These and other features of the present invention will be best understood from the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:

<figref idrefs="DRAWINGS">FIG. 1</figref> illustrates a schematic diagram of an apparatus for making the film of the present invention.

<figref idrefs="DRAWINGS">FIG. 2</figref> illustrates a film employed on a heat transfer component.

<figref idrefs="DRAWINGS">FIG. 3</figref> illustrates the particulate embedded in and adhered to the film.

<figref idrefs="DRAWINGS">FIG. 4</figref> illustrates the surface treated particulate embedded in and adhered to a film.

<figref idrefs="DRAWINGS">FIG. 5</figref> illustrates the particulate adhered to the film by an adhesive substance or a mixture of reactants.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to <figref idrefs="DRAWINGS">FIG. 1</figref>, an apparatus <b>10</b> for making a film <b>12</b> with improved wettability is illustrated. The film <b>12</b> is laminated to the metal heat exchanger of either a condensing furnace or an aluminum fin of an air conditioner evaporator shown schematically at <b>100</b> in <figref idrefs="DRAWINGS">FIG. 2</figref>. The metal heat exchanger <b>100</b> cools the fluid to a temperature below the dew point. As the temperature drops below the dew point, a liquid condensate, water vapor, condenses, transferring heat from the water vapor to the air.

By increasing the surface energy of the film <b>12</b>, the wettability of the film <b>12</b> can be increased and heat transfer can be improved.

The heated film <b>12</b> is extruded from a die <b>14</b>. The film <b>12</b> can be made of polyolefin, polyester, polyetherketone, polyetheretherketone, polysulfone, polyethersulfone, polytetrafluoroethlyne, or fluorinatedhydrocarbon. However, any thermoplastic film <b>12</b> which bonds or can be bonded to metal can be utilized.

While the film <b>12</b> is soft and heated, a polar particulate <b>16</b> is mechanically added to the upper surface <b>18</b> of the film <b>12</b>. The film <b>12</b> enters a roller assembly <b>20</b> which embeds and adheres the particulate <b>16</b> to the upper surface <b>18</b> of the film <b>12</b>. As the film <b>12</b> begins to pass over a large roller <b>22</b>, a first small roller <b>24</b> positioned over the large roller <b>22</b> presses the particulate <b>16</b> into the upper surface <b>18</b> of the film <b>12</b>. The temperature of the first smaller roller <b>24</b> is controlled to prevent the film <b>12</b> from cooling too fast.

As the film <b>12</b> continues to pass over the large roller <b>22</b>, the film <b>12</b> begins to cool. A second small roller <b>26</b> is positioned proximate to the large roller to retain the film <b>12</b> against the large roller as the film <b>12</b> cools. The temperature of the large roller is also controlled to insure that the film <b>12</b> has “set” when the film <b>12</b> leaves the roller assembly <b>20</b>.

The particulate <b>16</b> may be any polar material that embeds in and adheres to the upper surface <b>18</b> of the film <b>12</b>. The particulate <b>16</b> is partially exposed to create a polar surface on the upper surface <b>18</b> of the film <b>12</b>. The particulate <b>16</b> may be alumina, silica, zirconia, wollastonite, talc, titanium dioxide, or any other polar material.

At the molecular level, the polar particulate <b>16</b> is slightly charged and includes a positive ion and a negative ion. The condensed water vapor of the liquid condensate is also polar and includes a positive hydrogen ion and a negative hydroxide ion. The positive ion and the negative ion of the polar particulate <b>16</b> attracts the polar water molecules. For example, if the particulate <b>16</b> is titanium dioxide, the particulate molecule contains a positive titanium ion and two negative oxide ions. The positive titanium ion attracts the negative hydroxide ion of the condensate water vapor and the negative oxide ions attract the positive hydrogen ion of the condensate water vapor.

If titanium dioxide is utilized as the particulate <b>16</b>, it can also be employed as a germicide. As ultraviolet light contacts the titanium dioxide particulate, ozone is produced. The ozone kills bacteria, improving indoor air quality.

As illustrated in <figref idrefs="DRAWINGS">FIG. 3</figref>, after the particulate <b>16</b> is embedded in and adhered to the upper surface <b>18</b> of the film <b>12</b> and the film <b>12</b> cools, the lower surface <b>28</b> of the film <b>12</b> is attached to the metal surface <b>32</b> of a heat transfer component. The component could be a fin, a heat exchanger, or other heat transfer component. The film <b>12</b> is attached to the metal surface <b>32</b> by either an adhesive surface or a mixture of reactants <b>36</b> that polymerize in situ.

The embedded and adhered polar particulate <b>16</b> increases the surface energy and the wettability of the film <b>12</b>, allowing the liquid condensate to form as a layer rather than as droplets, which can be easily spread into the atmosphere.

In another embodiment, as shown in <figref idrefs="DRAWINGS">FIG. 4</figref>, a surface treatment <b>30</b> is added to the particulate <b>16</b> either to enhance adhesion of the particulate <b>16</b> to the polymer or to enhance wettability. Any surface treatment <b>30</b> can be utilized to enhance adhesion or wettability. If the film <b>12</b> is made of polyester, malcic anhydride can be utilized as the surface treatment <b>30</b>. The surface treatment <b>30</b> utilized on the particulate <b>16</b> varies depending on the chemistry of the film <b>12</b>.

In another embodiment, as illustrated in <figref idrefs="DRAWINGS">FIG. 5</figref>, the particulate <b>16</b> is adhered to the film <b>12</b> by a coating <b>34</b> of an adhesive substance or a mixture of reactants that polymerize in situ. The particulate <b>16</b> is pressed into and embedded into the coating <b>34</b> before curing.

By adhering polar particulates to a film laminated on the metal surface of a heat exchanger, a polar surface is formed. The polar surface increases the surface energy of the film and improves wettability. As liquid condensate forms in the heat exchanger, the liquid condensate spreads over the polar surface of the film rather than forming droplets which can spread into the atmosphere.

It is preferred that the extruded film <b>12</b> have a thickness between 0.1 mil and 10mils, or between 2.54 microns and 254 microns. It is also preferred that the polar particulate <b>16</b> have a size range between 0.25 microns and 100 microns. However, the size of the polar particulate <b>16</b> must correspond to the thickness of the film <b>12</b>. If the polar particulate <b>16</b> is too large for the thickness of the film <b>12</b>, the particulate <b>16</b> will not adhere to the film <b>12</b>. However, if the polar particulate <b>16</b> is too small for the thickness of the film <b>12</b>, the particulate <b>16</b> will become embedded into the film <b>12</b> and the polar surface will not protrude from the film <b>12</b>. The size of the particulate <b>16</b> also depends on the fluidity of the film <b>12</b> and the amount of pressure placed on the particulate <b>16</b> to adhere and embed the particulate into the film <b>12</b>.

The amount of particulate added to the surface of the film <b>12</b> also depends on the surface energy required. If the surface area is not required to be high, less particulate is needed. If the surface area is required to be high, more particulate is needed. If more particulate is added, the surface tension of the film can be increased. Therefore, the average surface energy of the film can be controlled by the number of particulates per the area of the film.

The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specially described. For that reason the following claims should be studied to determine the true scope and content of this invention.